This application relates to the field of automotive ignition systems. In particular, this application relates to an automatic shut-off circuit for an electronic ignition system.
There have been numerous attempts to provide devices to disable various automotive systems, including automotive ignition system, when the engine is not operating.
U.S. Pat. No. 1,878,313, issued to Pescara on Sept. 20, 1932, entitled "SAFETY CONTACT DEVICE FOR AUTOMOBILES", discloses a switch activated by oil pressure which opens when engine oil pressure drops.
U.S. Pat. No. 1,921,974, issued to Jolivet et al. on Aug. 8, 1933, entitled "SECURITY DEVICE FOR BATTERY IGNITION CIRCUITS", discloses the use of the time constant of a relay coil connected across breaker points of an ignition system, to either open the ignition circuit, or insert a current-limiting resistor in the ignition circuit if the breaker points have been open for a period of time.
U.S. Pat. No. 2,317,588, issued to Claytor et al. on Apr. 27, 1943, entitled "IGNITION SYSTEM", discloses the use of a bimetallic switch which opens in response to an electrical heater in series with automotive breaker points, which becomes hot when the points are closed for an excessive period of time, and causes the bimetallic switch to open and remove holding current from the coil of a relay switch.
U.S. Pat. No. 2,502,580, issued to McMillan on Apr. 4, 1950, entitled "ELECTRICAL CIRCUITS FOR MOTOR VEHICLES", discloses various circuits for disabling various automotive accessories, including the use of a relay switch which is closed by a starter switch and remains closed thereafter until the ignition switch is opened or various other conditions occur.
U.S. Pat. No. 2,790,841, issued to Sekul et al. on Apr. 30, 1957, entitled "PROTECTIVE ELECTRICAL SWITCHING SYSTEM", discloses the use of a time delay switch to disconnect a primary source of electric power from vehicle accessories after the ignition system has been deenergized.
U.S. Pat. No. 2,857,899, issued to Lardi on Oct. 28, 1958, entitled "AUTOMATIC IGNITION SHUT-OFF SWITCH", discloses the use of a combination of vacuum switch and solenoid switch to maintain operation of an automotive ignition system in response to generator output voltage or manifold vacuum.
U.S. Pat. No. 2,888,507, issued to Whitlow on May 26, 1959, entitled "AUTOMATIC SAFETY DEVICE FOR VEHICLES", discloses a structure for a time delay switch which is normally actuated to provide power to an ignition system by the ignition switch, and normally deactivated by a door switch.
U.S. Pat. No. 3,745,985, issued to Hohne on July 17, 1973 entitled "ARRANGEMENT FOR PREVENTING CURRENT FLOW IN THE IGNITION COIL OF AN INTERNAL COMBUSTION ENGINE DURING STANDSTILL CONDITIONS", discloses a circuit which differentiates pulses received from a magnetic pick up or breaker point to periodically discharge a capacitor. When the capacitor is no longer being discharged, the same switch which is opened to provide an ignition spark is opened to prevent current flow in the ignition coil.
U.S. Pat. No. 4,088,106, issued to Borst et al. on May 9, 1978, entitled "QUIESCENT CURRENT DISCONNECT SYSTEM AND APPARATUS FOR IGNITION COILS OF INTERNAL COMBUSTION ENGINE IGNITION SYSTEM", discloses the use of a digital logic circuit comparing a clock signal with a signal derived from a star-wheel transducer having three degree resolution, and disconnecting the ignition circuit when a counter circuit reaches a predetermined number before the next signal from the star-wheel transducer.
U.S. Pat. No. 4,106,460, issued to Kopera on Aug. 15, 1978, entitled "HALL EFFECT ELECTRONIC IGNITION CONTROL UNIT WITH AUTOMATIC SHUT-DOWN TIMER", discloses an ignition circuit having a capacitor which is charged when a first transistor is deenergized to provide a firing signal, and is discharged through a fixed signal, and is discharged through a fixed resistor. If the time between ignition impulses is too long, the voltage on the capacitor reaches the threshold of a programmable unijunction transistor, which shorts the base of the first transistor, deenergizing an ignition coil.
It is desirable to have an ignition circuit that will both remain energized for a sufficient time after the engine is stopped to provide an opportunity for making measurements for the purpose of testing and repair, and also disconnects the ignition coil, to prevent discharge of a storage battery, and over heating of the ignition coil and other components, without suddenly disconnecting the ignition coil so as to generate a spark. Generation of a single spark has been found sufficient to unexpectedly start a vehicle engine, causing damage and personel injury.